1. Field of the Invention
This invention relates to well tools used in the rotary drilling of wellbores, and it more particularly relates to a drill bit bottom hole contact and shock absorber device.
2. Background of the Invention
In the drilling of a wellbore, a rotary drill bit is employed for cutting away the formations being penetrated. The drill bit is suspended upon a drill string which can be of great lengths, e.g. 25,000 feet. Although the drill bit rotates at relatively low RPM, it can generate relatively large shock forces of both angular and axial directiveness that are applied to the drill string. These shock forces can cause physical injury to both the drill string and drill bit. Also, these shock forces prevent maintaining the drill bit in contact with the bottom of the wellbore. As a result, the efficiency of drilling can suffer from even small axial displacements (e.g., one half inch) of the drill bit from contact with the formation being penetrated. Likewise, angular shocks produce serious variations in the torque applied to the drill bit which results in non uniform formation penetration. Obviously, it is most desirable to prevent the angular and axial shock forces from the drill bit being applied to the drill string or effecting the bottom hole contact by the drill bit.
Various well tools have been proposed to have either bottom hole contact function or shock absorber functions. A few well tools have been proposed to provide a combination of such functions. In general, these combination tools use a helical connection in the well tool and a fluid dash pot or hydraulic cushion. As a result, these combination tools are very complex in construction and element functioning which leads to short operational lives, difficult field servicing, repairs and other undesirable results.
The present invention provides a well tool combining in function the bottom hole contact and shock absorber features but with a relatively simple construction, long life in well drilling and a relatively simple constructable and repairable structure.